In this study, the impacts of temperature-humidity index (THI), year and season were assessed on the performance of Holstein cows and their bulk milk portfolio at an Egyptian dairy farm using bulk tank milk data. The dataset involved 10,000 lactation records for Holstein cows, through the period from January 2019 to December 2020. The lower averages of DMI, DMY, and MFR were achieved at THI>72. Furthermore, the bacteriological parameters including TBC and coliforms count reached lower levels in bulk milk at THI≤72. The DMI and DMY were significantly affected by the year, while MFR and milk composition were not affected. The greatest averages of DMI, DMY and MFR were observed in winter and spring, while improved milk composition was achieved in winter and autumn. The DMI was significantly affected by THI with lower values when THI>72 for the fresh and high yielding cows. The DMY was significantly affected by THI>72 for all cows, however, the greatest effect was observed for the high yielding cows (31.81kg/day). High economic losses in daily milk production were recorded in the high producing cows at high THI>72 due to heat stress. The THI has a considerable impact on both the performance and bulk milk parameters of Holstein cows in Egypt with high economic losses in daily milk production especially in the high producing cows which are highly impacted by heat stress.